* Heliocentric (Astronomy) - Definition,meaning - Online Encyclopedia This entry contributed by Dana Romero Astronomical coordinates which use the center of the Sun as their origin. 10 Interesting Heliocentric Solar System Quotes Heliocentrism is the astro nomical model which places a stationary Sun at the center of the Solar System while the Earth , planet s and other bodies revolve around it. Heliocentric theory[edit] Teaching around 150 BC, he is known to have been a follower of the heliocentric theory of Aristarchus of Samos, which stated that the Earth rotate d around its own axis which in turn revolve d around the Sun . heliocentric model A mode of the solar system which is centered on the Sun , with the Earth in motion about the Sun . helioseismology The study of conditions far below the Sun 's surface through the analysis of internal "sound" waves that repeatedly cross the solar interior. Heliocentric Refers to a reference system centered at the sun . For example, the heliocentric distance to an object is the distance between the object and the sun 's center. Heliocentric With the Sun at the center.

Heliopause The gradual boundary between the heliosphere and the interstellar gas outside our solar system . See the diagram with the definition of " heliosphere " below. heliocentric having the Sun as the centre I inferior conjuction when an inferior planet passes between the Sun and the Earth so that they are lined up in the order Sun , inferior planet , Earth inferior planet a planet whose orbit is inside the Earth 's orbit around the Sun , namely, ... HELIOCENTRIC Having the Sun as a center, such as a heliocentric solar system . I IMPACT CRATER S Crater s which are the result of a collision between a large body, such as a planet or satellite , and a smaller body such as an asteroid or meteorite . Heliocentric. Centered on the Sun . Heliopause . The region in space where the Sun 's atmosphere merges with interstellar space . The position of the heliopause depends both on the strength of the solar wind and on the properties of the local interstellar medium . Heliocentric. Referring to the sun .

A heliocentric orbit is one based on the sun as one of the two foci of the ( elliptical ) orbit (or as the center of a circular orbit ); ... Heliocentric Helioseismology ... heliocentric universe (35) A model of the universe with the sun at the center, such as the Copernican universe. helioseismology (91) The study of the interior of the sun by the analysis of its modes of vibration. Heliocentric. Meaning: As seen from the centre of the Sun . A system of co-ordinates. Hertzsprung-Russell diagram . A diagram in which stars are plotted according to their spectral type and their absolute magnitude . Heliocentric - Centered on the Sun . In the heliocentric model of the solar system , the planet s move about the Sun Heliopause - The boundary of the heliosphere , where the solar wind merges into the interstellar gas ... heliocentric - (n.) Sun -centered; using the sun rather than the earth as the point to which we refer.

A heliocentric measurement, for example, omits the effect of the Doppler shift caused by the earth 's orbit al motion. heliocentric parallax Alternative name for annual parallax . See also diurnal parallax ; trigonometric ... Heliocentric model that replaced the geocentric Ptolemaic model , and was thus a considerable improvement. The model , however, still involved epicycle s and the spheres. [A84] Copernican Principle Copernican Revolution ... In the heliocentric model the 6 angles that just happened to always be the same in the geocentric model are all a reflection of the motion of the Earth around the Sun . This is a considerable simplification of the model . In his heliocentric theory, Copernicus found himself able to describe the movements of the Moon and planet s in a more elegant way than Ptolemy in his geocentric system . Both model s employed perfect circular motion with epicycle s, equant s ... Nikolas Kopernig ( Copernicus , 1473-1543) ...

Copernicus ' heliocentric model Heliocentrism In astronomy , heliocentrism is the theory that the Sun is at the center of the Universe. The word came from the Greek language . Historically, heliocentrism was opposed to geocentrism, which placed the earth at the center.... Copernicus - heliocentric theory of the universe Roman Empire Julian calendar ( solar calendar ) ... Figure 2-1. Heliocentric Orbit s of Mars and Earth showing the relative positions of both planet s in their respective orbit s around the Sun measured in degrees. The inner rings are the season of Earth and the outer ring is the season s for Mars . ... heliocentric Relative to the sun as a center, as a heliocentric orbit . heliocentric parallax The difference in the apparent positions of a celestial body outside the solar system , as observed from the earth and sun . Also called stellar parallax . See parallax . heliocentric (universe): model of the universe with the Sun at the center and all other objects moving around it. helioseismology the study of the Sun 's interior from observations of the Sun 's pulsations on its surface.

heliocentric Sun centered; see Copernicus , Kepler , Galileo. heliopause The point at which the solar wind meets the interstellar medium or solar wind from other stars. heliosphere The space within the broundary of the heliopause containing the Sun and solar system . The Greeks also tried to derive the distance of the Sun , starting the road to heliocentric theory, with roles by Ptolemy, Copernicus , Galileo and Kepler . However, it did put heliocentric views out in the restricted open, and it was useful to people such as Galileo to help revolution ize astronomy in Europe. ISEE C was launched into a heliocentric orbit and will make observations in the solar wind up stream of the Earth . Used for International Comet ary Explorer. Copernicus , Nicolaus 1473-1543 Polis h astronomer who advanced the heliocentric theory that the Earth and other planet s revolve around the Sun . His observations helped consolidate the Copernican concept of a heliocentric model . He also made valuable contributions to the phsyics of motion. galaxy A huge collection of stars - often many thousands of millions - and associated dust and gas.

A topocentric datum is measured from the surface of the Earth , and a heliocentric one is measured from the center of the Sun . Get Ax.0 data Shift-F11 If you have the ten-CD set of USNO A1.0 disks, or the eleven-CD set of A2.0 disks, or the single-CD SA1.0 or SA2. R: The alphabetic letter ("variable") used to denote the distance between the sun and the object being discussed, also called the object's heliocentric distance; in most ephemerides of objects such as comet s and minor planet s, r is given in AU. Aphelion distance Abbreviation Q, distance of greatest heliocentric separation for a body in an eccentric orbit ; Q=a(1+e). Apollo asteroids Asteroids having semimajor axes a1. Heliocentric Universe - The 3rd Century B.C. Greek astronomer and mathematician Aristarchus of Samos was the first to present an explicit argument for a heliocentric model of the Solar System , placing the Sun , not the Earth , at the center of the known universe.

There matter s might have stood were it not for the fact that that object was located at the heliocentric distance predicted by Bode's law of planet ary distances proposed in 1766 by the German astronomer Johann D. Titius and popularized by his compatriot Johann E. Annual parallax , the greatest value of the heliocentric parallax , or the greatest annual apparent change of place of a body as seen from the earth and sun ; as, the annual parallax of a fixed star . Galilei (Galileo) Italian physicist and astronomer (1564-1642 A.D.), reported the first astro nomical observations using a telescope he made himself, studied the laws of motion, and was a fervent defender of Copernicus ' heliocentric system . Gaseous planet Also known as Jovian planets . He knew that talking about a heliocentric model was not only bad philosophically (since it went against Aristotle) and religiously (since the church preferred a geocentric model ), but promoting a heliocentric model could also be fatal.

he rejected the possibility of interpenetrating spheres, but for some reason thought Martian parallax at opposition is greater than solar parallax , whereby Mars must then be nearer the Earth than the sun is, but also whereby the Martian and solar spheres must intersect on all geocentric and geoheliocentric ... The 681 million km heliocentric cruise to Mars will take approximately 10 month s, with landing on Mars on 25 May 2008. Nominal times are given, these are subject to change by up to about a minute. Tycho G moves at -108 km/sec (heliocentric) in the radial direction. In contrast, all other stars with distances compatible with that of SN 1572 have radial velocitites within the velocity dispersion as compared with the average of all stars at the same location in the Galaxy (see Figure 4). . . . Aristarchus of Sï¿½mos (310?BC-250?BC) was an ancient Greek astronomer who was the first person to propose a heliocentric model of the Solar System .

Aristarchus realized that the Earth rotate s on its axis and revolve s around the Sun . Both spacecraft comprising the mission carry a Heliocentric Imager (HI) with cameras (HI-1 and HI-2I) built and developed at the STFC's Rutherford Appleton Laboratory and the University of Birmingham. The Heliocentric System In a book called On the Revolution s of the Heavenly Bodies (that was published as Copernicus lay on his deathbed), Copernicus proposed that the Sun , not the Earth , was the center of the Solar System . Such a model is called a heliocentric system . German mathematician and astronomer Johannes Kepler (1571-1630) also helped to refine the heliocentric model with his introduction of elliptical orbit s. In the 16th century Nicholas Copernicus proposed a heliocentric system in which the Earth rotate d on its axis , and along with the other planet s, orbit ed the Sun . But the observational evidence of the time favoured the epicycle -based Ptolemaic system .

Often some form of spherical or rectangular system is used (although phase space coordinates and null-geodesic lattices are popular in some regions), with heliocentric, local or planet ary origins and wildly different ideas about measurement scales and ca libration directions. Copernicus is most famous for inventing the Copernican system , which is also known as the heliocentric theory. The Copernican system is a model for our Solar System in which the Earth and all other planet s orbit around the Sun and the Sun is the center of the universe. So in the 1540s we had Copernicus publishing his heliocentric theory of the universe. Then in the 1570s we had Tycho Brahe building a new observatory and working very carefully to mark positions, to map the sky , to study planet ary motions with greater precision than had previously ever been done. " The idea of a heliocentric or sun -centered system is considered so important to history that it is often referred to as the " Copernican Revolution ." Once we accept that the Sun is a star , we immediately are confronted with the possibility that the galaxy is filled with suns and planet s. Sun -centered.

The first to suggest the Heliocentric theory of gravitation was the Greek philosopher Aristarchus of Samos in the 4th century B.C. who put forth the then-radical view that Earth and other planet s revolve around the Sun . Nicolaus Copernicus , who was the first to propose a comprehensive heliocentric cosmology , displacing the Earth from the centre of the universe, also made numerous observations of Spica while researching precession . Let's reduce the problem to two dimensions and ask wh ether all the planet s can have the same heliocentric longitude (they can never line up in three dimensions because their orbit al planes are all slightly different). Nicolaus Copernicus (1473 - 1543): He was a Polis h physician and lawyer by trade, but is now regarded as the father of the current heliocentric model of the solar system . An interesting historical fact, is that the phases of Venus were discovered by Galileo with what was at the time among the first telescope s. And that was a major argument for the heliocentric model of the solar system ...

When German theologian David Fabricius discovered it in 1596, this put a new dent in the notion of unchangeability of the heavens, undermining the Ptolemaic model and shifting in favour of the Copernican Revolution and the heliocentric model . Mira was named by Polis h astronomer Johannes Hevelius. Many believed the sun revolve d around the Earth , with ancient Greek scholar Ptolemy formalizing this " geocentric " model in 150 B.C. Then, in 1543, Nicolaus Copernicus described a heliocentric, sun -centered model of the solar system , and in 1610, Galileo Galilei 's discovery of Jupiter ' ... recount the life of Copernicus , including his sometimes mundane day job as a Catholic church administrator and physician to the Bishop of Varmia. Sobel shows how, despite his duties, Copernicus patiently measured motions of the moon and planet s for decade s, slowly building evidence for his heliocentric theory ...

Claudius Ptolemaeus or Ptolemy (about 87-150) was a Greek astronomer and mathematician who wrote about his belief that all celestial bodies revolve d around the Earth . His writings influenced people's ideas about the universe for over a thousand years, until the Copernican System (with a heliocentric solar ... Inferior conjunction s taking place in March always find Venus far north of the Sun . Yes, even though Venus ' greatest heliocentric latitude is only 3.4o, it's geocentric latitude at inferior conjunction can exceed 8o 50'. The diagram below helps to illustrate. Parsec (pc) The distance an object would haveto be from the earth so that its heliocentric parallax would be 1 second of arc; equal to 3.26 light year s; a kiloparsec is 1000 parsec s. 1000+ images about Aristarchus of Samos on Pinterest | Models, Aristarchus of samos and Solar system Forward Mysterious Aristarchus: Hunting for the man who first got it right.

Aristarchus of Samos, born in 310 BCE, pondered the sky and arrived at correct conclusions 18 centuries ahead of everyone else. Aristarchus was a mathematician and astronomer, and the very first person to write and preach that the Sun is the center of the solar system, and that Earth orbits around it while also spinning like a top. To his contemporaries, it must have seemed nothing short of crazy. See More Who Discovered The Earth Moves Around The Sun? Home Astronomy History Who Discovered The Earth Moves Around The Sun? Who Discovered The Earth Moves Around The Sun? November 29, 2012 Peter Christoforou Astronomy History , FAQs 24 Copernicus (1473-1543) was not the first person to claim that the Earth rotates around the Sun. In Western civilization, ancient Greek astronomer Aristarchus of Samos is generally credited with being the first person to propose a Sun-centred astronomical hypothesis of the universe ( heliocentric ).

At that time, however, Aristarchus’s heliocentrism gained few supporters and 18 centuries would then pass before Renaissance astronomer Nicolaus Copernicus produced a fully predictive mathematical model of a heliocentric system. ANCIENT TIMES Yajnavalkya (9th Century BCE) Before the Golden Age of Greece, speculation that the Sun and not the Earth lay at “the centre of the spheres” dates back at least to the time of the Indian philosopher Yajnavalkya (9th Century BCE), who was part of a Vedic Tradition which used mathematics and geometry in some religious rituals. As Yajnavalkya wrote in a sacred Hindu text (Shatapatha Brahmana: 8.7.3.10): “The sun strings these worlds – the earth, the planets, the atmosphere – to himself on a thread.” This is one of the first recorded references to heliocentrism, but once again supporters of the idea were in the minority and India continued to believe in a geocentric model until the telescope was invented in the 17th century.

Aristarchus (310BC–230 BCE) In the days of Aristarchus our solar system was considered to be the whole of the known universe, with the Earth placed at its centre, and the rest of the planets and fixed stars revolving around the Earth daily.

According to Aristarchus’ revolutionary new theory, however, it was the Sun, not the Earth, which inhabitated its centre, while the Earth, and the rest of the planets orbited around the Sun in a circular motion, Unfortunately, Aristarchus’ one work which did survive from ancient times makes no mention of his heliocentric model, and so his ideas on the subject have had to be pieced together from references by such important figures as the Greek biographer Plutarch, the Greek philosopher Sextus Empiricus, and Greek mathematician Archimedes, who wrote in his book “The Sand Reckoner”: “His hypotheses are that the fixed stars and the Sun remain unmoved, and that the Earth revolves about the Sun in the circumference of a circle, the Sun lying in the middle of the orbit.” Nevertheless, the concept of a heliocentric model of the solar system seemed counter-intuitive to the senses and also encountered fierce resistance from religions which saw God’s chief creation man placed at the centre of the universe.

Plato, Aristotle And Ptolemy Consequently, the geocentric model of the solar system with the Earth placed at its centre proposed by such Greek philosophers as Plato (428-348 BCE), and Aristotle (384–322 BCE) became the accepted version of celestial events. In 140 AD the geocentric model was then cataloged by Ptolemy (90–168 AD) in his masterpiece entitled ‘Almagest’ which then became the established belief in the western world for the next 14 centuries. THE RENAISSANCE Copernicus (1473-1543) In 1543, Renaissance mathematician and astronomer Nicolaus Copernicus tried to revive Aristrachus’ heliocentric theory, but fear of being branded a heretic by the Christian Church meant he waited until his deathbed before publishing De revolutionibus. In his seminal work Copernicus formulated a fully predictive model of the universe in which the Earth is just another planet orbiting the Sun.

The Copernican Revolution which ensued is now seen as the launching point to modern astronomy, although at the time the Catholic church forbade Copernicus’ book and vehemently tried to suppress all arguments relating to his theory. Galileo Galilei (1564-1642) The next century, Galileo Galilei (1564-1642) used the newly invented refracting telescope to further expand on Copernicus’ theory, and in 1632 he published a book in which he openly stated that the Earth revolves around the Sun. In his book entitled ‘The Dialogue Concerning the Two Chief World Systems,’ Galileo compared the Copernican system with the Ptolemaic system, but was subsequently convicted on “grave suspicion of heresy”, forced to recant his beliefs, and subsequently spend the rest of his life under house arrest. Sir Isaac Newton (1643-1727) After Sir Isaac Newton invented the reflecting telescope in 1688, it soon became eminently clear that the Earth was not the centre of our solar system.

The final nail in the coffin of geocentrism then came after Newton published his Principia Mathematica in which he definitively proves the heliocentric model first proposed by Copernicus. Edmund Halley (1656-1742) would later use Newton’s equations to predict the return of a comet in 1758 to give final proof to the heliocentric theory. I will now leave you with a beautiful astronomy quote from Copernicus’ ‘De revolutionibus orbium coelestium’ published on his death bed in 1543, which states: “In the center of all rests the Sun. For who would place this lamp of a very beautiful temple in another or better place than this from which it can illuminate everything at the same time?” History of Astronomy History of Astronomy: Early Man -> little recorded information on early man's impression of the heavens, some drawings of eclipses, comets, supernovae such as the Pueblo Petrograph.

Early man was frightened/overwhelmed by the sky Early man also believed that the heavens held power over earthy existence (psychology of the unknown) -> origins of astrology as an attempt to understand, predict and influence events The earliest written records (i.e. history) were astronomical observations - Babylonians (~1600 B.C.) recorded position of planets, times of eclipses, etc. - also evidence from early Chinese, Central American and North European cultures such as Stonehenge , which is a big computer for calculating the position of planets and the Sun (i.e. when to have that big blowout Solstice thing) -> thus, Astronomy was the 1st science Hellenistic Culture (~500 B.C.): The ancient Greeks inherited astronomical records from the Babylonians and applied the data to construct a cosmological framework. Data was not just used for practical goals, such as navigation, but also to think of new experiments = natural philosopher. Thales (~480 B.C.) used this data to predict eclipses . Eratosthenes (220 B.C.) - The early Greeks knew the Earth was a sphere based on the shadow of Earth on the Moon during lunar eclipses.

Eratosthenes proceeded to use this information to measure circumference of Earth in the following manner; he knew that on a certain date that a stick placed in the ground at Syene cast no shadow. Whereas, a stick at Alexandria has a small shadow. Using simple ratios he showed the following: Hipparchus (100 B.C.) produced first star catalog and recorded the names of constellations . Heraclides (330 B.C.) developed the first Solar System model, beginning of the geocentric versus heliocentric debate Note that orbits are perfect circles (for philosophical reasons = all things in the Heavens are "perfect") Aristarchus (270 B.C.) developed the heliocentric theory Problems for heliocentric theory: Earth in motion??? can't feel it no parallax seen in stars geocentric = ego-centric = more "natural" Ptolemy (200 A.D.) was the Librarian of Alexandria who resurrected Heraclides geocentric theory and combined with centuries of data on planetary motions -> formulated complete description of the Solar System that explained/predicted the apparent motions.

The Ptolemic system began the 1st paradigm or framework for our understanding of Nature Unfortunately, the Ptolemy framework was extremely complicated in order to explain retrograde motion. The solution to retrograde motion was to use a system of circles on circles to explain the orbits of the planets called epicycles and deferents. The main orbit is the deferent, the smaller orbit is the epicycle. Although only one epicycle is shown in the figure below, over 28 were required to explain the actual orbits of the planets. In the Ptolemaic system, deferents were large circles centered on the Earth, and epicycles were small circles whose centers moved around the circumferences of the deferents. The Sun, Moon, and planets moved around the circumference of their own epicycles. In the movable eccentric, there was one circle; this was centered on a point displaced from the Earth, with the planet moving around the circumference. These were mathematically equivalent schemes. Although Ptolemy realized that the planets were much closer to the Earth than the "fixed" stars, he seems to have believed in the physical existence of crystalline spheres, to which the heavenly bodies were said to be attached.

Outside the sphere of the fixed stars, Ptolemy proposed other spheres, ending with the primum mobile ("prime mover"), which provided the motive power for the remaining spheres that constituted his conception of the universe. His resulting solar system model looked like the following, although the planets had as many as 28 epicycles to account for all the details of their motion. This model, while complicated, was a complete description of the Solar System that explained, and predicted, the apparent motions of all the planets. The Ptolemic system began the 1st mathematical paradigm or framework for our understanding of Nature. Alexandria burns, Roman culture collapses, Dark Ages... but the Roman Catholic Church absorbs Aristotle's scientific methods and Ptolemy's model into its own doctrine. Thus, preserving the scientific method and Ptolemy's Solar System until the... The Renaissance , where new ideas were more important than dogma. Copernicus (1500's) reinvented the heliocentric theory and challenged Church doctrine. The heliocentric model had greater depth than simply an improvement to solve retrograde motion, it also had social and political consequences.

For example, the Bible states (Psalm 93, addressing God) "Thou hast fixed the earth immovable and firm", which implies a geocentric model. Also, Joshua commanded the Sun to stand still, not the Earth. Heliocentric theory questioned the authority of the most revered wise men of the ancient world and the outcry over his ideas had little to due with the impersonal concern for truth. By placing the Sun at the center of the Solar System, Copernicus forced a change in our worldview = paradigm shift or science revolution . However, Copernicus also used circular orbits and had to resort to epicycles and deferents to explain retrograde motions. In fact, Copernicus was forced to use more epicycles than Ptolemy, i.e. a more complicated system of circles on circles. Thus, Copernicus' model would have failed our modern criteria that a scientific model be as simple as possible ( Occam's Razor ). Tycho Brahe (1580's) was astronomy's 1st true observer.

He built the Danish Observatory (using sextant's since telescopes had not been invented yet) from which he measured positions of planets and stars to the highest degree of accuracy for that time period (1st modern database). He showed that the Sun was much farther than the Moon from the Earth, using simple trigonometry of the angle between the Moon and the Sun at 1st Quarter. Tycho's measurements were used to show that there was no detectable parallax with the naked eye, in support of the geocentric theory. So, even though his observations were the best for his time, his result was wrong, a lesson in how science is done. Kepler (1600's) a student of Tycho who used Brahe's database to formulate the Laws of Planetary Motion which corrects the problems of epicycles in the heliocentric theory by using ellipses instead of circles for orbits of the planets. The formulation of a highly accurate system of determining the motions of all the planets marks the beginning of the clockwork Universe concept, and another paradigm shift in our philosophy of science. Galileo (1620's) developed laws of motion (natural versus forced motion, rest versus uniform motion).

Then, with a small refracting telescope (3-inches), destroyed the the idea of a "perfect", geocentric Universe with the following 5 discoveries: spots on the Sun mountains and "seas" (maria) on the Moon Milky Way is made of lots of stars Venus has phases Jupiter has moons (Galilean moons: Io, Europa, Callisto, Ganymede) Newton (1680's) developed the law of Universal Gravitation, laws of accelerated motion, invented calculus (math tool), the 1st reflecting telescope and theory of light. ... off to the 18-20th century, with discovery of the outer planets and where astronomy moves towards discoveries in stellar and galactic areas, next paradigm shift occurs in early 1960's with NASA deep space probes ARISTARCHUS ARISTARCHUS OF SAMOS ( 310 - 230 B.C. ) Aristarchus was a Greek Astronomer and Mathematician, born on the island of Samos, in the ancient Greece. He is considered the first person to propose a heliocentric model of the solar system.

The only work of Aristarchus which has survived to the present time is "On the Sizes and Distances of the Sun and Moon" Aristarchus argued that the Sun, Moon and Earth form a near right triangle at the moment of first or last quarter moon. He estimated that the angle (b) was 87 degree. Using correct geometry concluded that the Sun was 20 times farther away than Moon. Aristarchus also figured out how to measure the size of the Moon and Sun during a lunar eclipse. While sound in theory, in practice this procedure is highly inaccurate. This is because Earth - Moon distance is much smaller than Earth - Sun distance, implying that (b) is very close to 90 degree, so that (c) is in turn very small. This has the consequence that a small measurment error on (b) translates in a large variation in the ratio Earth-Moon/Earth-Sun. Aristarchus measured b=87 degree, while the true value is in fact 89 degree and 50 minutes.

This may seen a small error, but because of the large error amplification, Aristarchus' value leads to Earth-Sun/Earth-Moon=19 instead of the true value Earth-Sun/Earth-Moon=397. Nonetheless, Aristarchus' calculation was the first to mathematically set the spatial scale of the cosmos and his estimate showed that the Sun is much further away from us than Moon is. Copernicus himself originally gave credit to Aristarchus in his own heliocentric treatise, "De revolutionibus caelestibus", where he had written, "Philolaus believed in the mobility of the earth, and some even say that Aristarchus of Samos was of that opinion." Interestingly, this passage was crossed out shortly before publication, maybe because Copernicus decided his treatise would stand on its own merit. Aristarchus - Crystalinks Aristarchus (310 BC - circa 230 BC) was a Greek astronomer and mathematician, born in Samos, Greece.

He is the first recorded person to propose a heliocentric model of the solar system, placing the Sun, not the Earth, at the center of the known universe (hence he is sometimes known as the "Greek Copernicus"). His astronomical ideas were not well-received and were subordinated to those of Aristotle and Ptolemy, until they were successfully revived and developed by Copernicus nearly 2000 years later. Heliocentrism The only work of Aristarchus which has survived to the present time, On the Sizes and Distances of the Sun and Moon, is based on a geocentric worldview. We know through citations, however, that Aristarchus wrote another book in which he advanced an alternative hypothesis of the heliocentric model. Aristarchus thus believed the stars to be infinitely far away, and saw this as the reason why there was no visible parallax, that is, an observed movement of the stars relative to each other as the Earth moved around the Sun. The stars are in fact much farther away than was assumed in ancient times, which is why stellar parallax is only detectable with telescopes.

But the geocentric model was assumed to be a simpler, better explanation for the lack of parallax. Size of the Moon Aristarchus observed the Moon moving through the Earth's shadow during a lunar eclipse. He estimated that the diameter of the Earth was 3 times the Moon's diameter. Using Eratosthenes' calculation that the Earth was 42,000 km in circumference, he concluded that the Moon was 14,000 km in circumference. The Moon has a circumference of about 10,916 km. Distance to the Sun Aristarchus argued that the Sun, Moon, and Earth form a near right triangle at the moment of first or last quarter moon. He estimated that the angle was 87�. Using correct geometry, but inaccurate observational data, Aristarchus concluded that the Sun was 20 times farther away than the Moon. The true value of this angle is close to 89� 50', and the Sun is actually about 390 times farther away. He pointed out that the Moon and Sun have nearly equal apparent angular sizes and therefore their diameters must be in proportion to their distances from Earth.

He thus concluded that the Sun was 20 times larger than the Moon. This is also incorrect, although logical. It does, however, suggest that the Sun is clearly larger than the Earth, which can be taken to support the heliocentric model. The Geocentric Model of the Solar System | Wordsmith Insightful journalism and powerful fiction The Geocentric Model of the Solar System An Introduction to Ptolemaic Astronomy Geocentrism is an astronomical theory, central to the astronomy of Ancient Greece that posits that the Earth lies at the centre of the universe. The Geocentric model of the Solar System entered Greek astronomy sometime in the 6th Century BC in the writings of the astronomer Anaximander. Anaximander proposed a cosmological model of the universe, in which the Earth was shaped like a like a section of a pillar and held aloft at the centre of the universe. He is also believed to have been the first person to propose that the sun and the planets orbit the Earth. Anaximander also believed that the sun, moon, stars and planets were actually invisible wheels with holes in them, that revealed a concealed fire.

The Geocentric Model in Greek Astronomy In the 4th Century BC, Plato, and his student Aristotle, wrote a number of important treatises about the Geocentric Model of the Solar System. According to Plato, the Earth was a stationary sphere at the centre of the universe. He also believed that the sun, moon and planets orbited the Earth on individual spheres, which he believed explained the circular motion of the stars and planets. Adherence to the Geocentric Model of the Solar System was the result of a number of important observations. The first was that if the Earth was moving, it should be possible to observe the phenomenon known as stellar parallax, an optical trick that seems to shift the position of the sun, moon and planets. This was believed to be the case because the shapes of the constellations do not change over the course of the year. The second important observation was that the brightness of Venus does not vary. To the Greeks, this implied that the distance between the Earth and the planets was constant. The only way this could be explained was if the Earth did not move.

However, one of the major flaws of Geocentrism that the Greeks could not explain was the variation in brightness of the other planets, over the course of the year. Sometime around 150 AD, the ideas of Anaximander and other Geocentric astronomers were collected and codified by the Roman astronomer Claudius Ptolemy. For this reason, the Geocentric model is also sometimes called the Ptolemaic model. Not all Greek astronomers supported the Geocentric view of the universe, however. The followers of Pythagoras believed that numbers had divine meaning. As a result, the followers of Pythagoras worshipped a symbol they called the Monad, a single dot within a circle. They believed that the dot represented represented the gods at the centre of the universe and that the circle represented the orbits of the planets. The Greek astronomer Heraclidies Ponticus also wrote a treatise, in which he claimed that the planets orbited the sun and that the sun orbited the Earth. Around the same time, another Greek astronomer, Aristarchus of Samos, wrote a treatise arguing for a heliocentric model of the Solar System.

However, his theories were not widely accepted and no copies of his writing have survived. Geocentrism would not be seriously challenged until the 16th Century. The Geocentric Model and the Coperican Revolution In 1543, the Polish astronomer Nicolaus Copernicus published a paper entitled, On the Revolution of Heavenly Spheres. He set out to mathematically demonstrate the viability of a heliocentric solar system, where the planets orbit the sun, instead of the other way around. Because the Heliocentric, or Copernican model of the solar system could not offer better predictions for eclipses and planetary alignments, Copernicus’s ideas were slow to gain acceptance. Following the invention of the telescope, in 1609, observations made by the Italian astronomer Galileo called some of the basic tenets of Geocentrism into question. Starting in December, 1610, Galileo became the first person to observe the phases of Venus. The Geocentric model of the Solar System states that if Venus is between the Earth and the sun, then Venus should be in continuous darkness. The discovery of the phases of Venus represented the first serious challenge to Geocentrism.

The observations of Galileo and Copernicus eventually led to the discovery of the Three Laws of Planetary Motion by Johannes Kepler between 1609 and 1619. Based on the concept of a heliocentric universe, Kepler was the first person to successfully predict the transit of Venus across the face of the sun. In 1687, Sir Isaac Newton devised his law of universal gravity using theories developed by Kepler, Tycho Brahe and Galileo. In 1838, German astronomer Fredich Wilhelm Bessel measured the stellar parallax of the star 61 Cygni, disproving the Geocentric ascertation that such a phenomenon did not exist. Today, a geocentric framework is still useful in some applications, such as navigation at sea and in planetariums. However a geocentric understanding of the universe is generally not useful for the computation of planetary orbits or spacecraft trajectories. Today astronomers think of the Solar System as being in motion relative to the motion of the Milky Way Galaxy. Sources Crowe, Michael J. (1990).Theories of the World from Antiquity to the Copernican Revolution. Mineola, NY: Dover Publications, Inc.

Evans, James. The History and Practice of Ancient Astronomy. New York: Oxford University Press, 1998. Walker, Christopher, ed. Astronomy before the telescope. London: British Museum Press, 1996 Michael Hoskin, The Cambridge Concise History of Astronomy, Cambridge University Press, 1999 Share this: Aristarchus - Oakton Astronomy Animation Website Oakton Astronomy Animation Website Home ‎ > ‎ Astronomers and Other Great Scientists ‎ > ‎ Aristarchus Aristarchus of Samos lived from approximately 310 BCE to 230 BCE. He was a Greek mathematician and astronomer. He is best known today as the first person known to propose a heliocentric model of the Solar System (effectively the Universe for ancient times). Aristarchus believed that the angle made between the center of the Earth, the center of the Sun, and the terminator of the First Quarter Moon was about 87 degrees. Since the Sun and Moon had about the same angular size (witness the Moon covering the Sun perfectly during a Total Solar Eclipse), this angle could be used to gemetrically determine the ratio of the Earth-Moon distance to the Earth-Sun distance.

Using the angle of 87 degrees, Aristarchus concluded that this distance ratio is about 19, thereby suggesting that the Sun's diameter must be at least seven times greater than the Earth's. Today we know that this distance ratio is actually close to 400 (and that the above mentioned angle is about 89.5 degrees), and that the Sun's diameter is almost 110 times greater than Earth's. It was from this "distance ratio reasoning" that Aristarchus correctly concluded that the Sun must be the most massive object in the Solar System, and that it must therefore be at the center of the Solar System. Unfortunately, a lack of understanding amongst his contemporaries of how truly far away the so-called "fixed" stars were, and why they therefore did not exhibit at least some visible parallax relative to each other, caused them to reject Aristarchus' heliocentric explanation of the Solar System. It would be another 1800 years before the Polish cleric Copernicus would revisit his idea. To the left is a drawing that illustrates Aristarchus' idea of how the "Sun to Earth to First Quarter Moon" angle could be used to find the above mentioned distance ratio.

Click on the image to enlarge it, so that you can study it. Note that the inverse of the sine of 3 degrees is about 19.

Question: Which Greek astronomer was the first person to formally propose the heliocentric model of the solar system?
Answer: ARISTARCHOS